Defective product inspection apparatus, probe positioning method and probe moving method

ABSTRACT

For adjusting a positional relationship between a specimen and a probe to measure an electric characteristic of the specimen through a contact therebetween, a base table holding a specimen table holding the specimen and a probe holder holding the probe is positioned at a first position to measure the positional relationship between the probe and the specimen at the first position, and subsequently positioned at a second position to measure the positional relationship therebetween at the second position so that the probe and the specimen are contact each other at the second position, the specimen table and the probe holder are movable with respect to each other on the base table at each of the first and second positions to adjust the positional relationship between the probe and the specimen, and a measuring accuracy at the second position is superior to a measuring accuracy at the first position.

RELATED APPLICATIONS

This application is a Divisional of U.S. Application No. 11/976,238,filed Oct. 23, 2007, now U.S. Pat. No. 7,553,334, which is aContinuation of U.S. application Ser. No. 11/002,710, filed Dec. 3,2004, now U.S. Pat. No. 7,297,945. which claims priority of JapaneseApplication No. 2003-406707, filed Dec. 5, 2003. the entire contents ofeach of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a defective product inspectionapparatus (probe apparatus), a probe positioning method and a probemoving method, for measuring an electric characteristic of a microscopicarea of an electronic element.

A defective product inspection apparatus is well known as the prior art,in which a probe contacts an area of a specimen (an electronic element)at which an electric characteristic needs to be inspected. An electriccurrent-voltage characteristic or the like of the electronic element canbe measured through the probe.

JP-A-9-326425 discloses that a probe is arranged in a specimen chamberof a scanning electron microscope (SEM) to measure a minute electricpotential characteristic.

JP-A-2000-147070 discloses a probe apparatus in which a probeinformation image showing an information for operating desirably a probeis formed on a display, a specimen and the probe are shown in the probeinformation image on the display, a probe operating image area formoving the probe is formed on the display, the probe is moved through aprobe controller in accordance with an operating signal from the probeoperating image area, and a movement amount from an actual currentposition of a front end of the probe to a target position thereof iscalculated by designating each of the actual current position of thefront and of the probe and the target position of the front and of theprobe on the probe information image so that the probe controlleroperates in accordance with the movement amount to move the probe to thetarget position.

JP-A-2000-181898 discloses a probe apparatus including a chargedparticle beam projection device, a specimen stage for holding a specimenholder with a specimen thereon, a specimen chamber containing thespecimen stage, a probe driving mechanism for moving the probe tocontact the specimen in the specimen chamber, a specimen antechamberincluding a first stocker connected through a valve to the specimenchamber to store temporarily the specimen holder, and a first transferdevice for moving the specimen holder at least between the specimenantechamber and the specimen chamber.

JP-A-2002-523784 discloses that an optical microscope slides on amicroscope bridge to move to a position on a wafer chuck, and is rotatedto a position for preventing from standing in the way of enabling theprobe to firstly be positioned in an area of the specimen to which anuser's attention is drawn.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a defective productinspection apparatus and method for adjusting a positional relationshipbetween a specimen and a probe, by which apparatus and method anelectric characteristic of the specimen can be measured efficiently(with making a time period needed for the inspection as small aspossible) while the specimen is restrained from being damaged.

According to the invention, a defective product inspection apparatus formeasuring an electric characteristic of a specimen through (or with) acontact between a probe and the specimen (so that the measured electriccharacteristic is compared with a predetermined electric characteristicto judge whether the specimen as a product is defective or not),comprises, a specimen table for holding the specimen thereon, a probeholder for holding the probe thereon, a first measuring device formeasuring a positional relationship between the probe and the specimen,and a second measuring device for measuring the positional relationshipbetween the probe and the specimen, wherein (a measuring accuracy(resolution capability, magnification or the like) of the secondmeasuring device is superior to a measuring accuracy (resolutioncapability, magnification or the like) of the first measuring device,)the apparatus further includes a base table holding thereon the specimentable and the probe holder in such a manner that the specimen table andthe probe holder are movable with respect to each other on the basetable to adjust the positional relationship between the probe and thespecimen on the base table so that a contact area of the probe and adesired area of the specimen are capable of being brought into contactwith each other, and the base table is movable between (or from) a firstposition at which the positional relationship between the probe and thespecimen is measurable by the first measuring device and (or to) asecond position at which the positional relationship between the probeand the specimen is measurable by the second measuring device.Incidentally, the specimen table is movable with respect to the basetable, and the probe holder is movable with respect to the base table,so that a positional relationship between the specimen table and thebase table and a positional relationship between the probe holder andthe base table are adjustable independent of each other, and one of thepositional relationship between the specimen table and the base tableand the positional relationship between the probe holder and the basetable is adjustable when the other one the positional relationshipbetween the specimen table and the base table and the positionalrelationship between the probe holder and the base table is stationary.

Since (the measuring accuracy of the second measuring device is superiorto the measuring accuracy of the first measuring device, and) the a basetable holding thereon the specimen table and the probe holder in such amanner that the specimen table and the probe holder are movable withrespect to each other on the base table to adjust the positionalrelationship between the probe and the specimen on the base table sothat a contact area of the probe and the desired area of the specimenare capable of being brought into contact with each other, and the basetable is movable between (or from) the first position at which thepositional relationship between the probe and the specimen is measurableby the first measuring device and (or to) the second position at whichthe positional relationship between the probe and the specimen ismeasurable by the second measuring device, a time period which is neededfor measuring the positional relationship between the probe and thespecimen at the second position with the measuring accuracy superior tothe measuring accuracy at the first position can be decreased by themeasurement at the first position, so that the electric characteristicof the specimen can be measured efficiently. If the probe and thespecimen are brought into contact with each other at the secondposition, a time period which is needed for bringing the probe and thespecimen into contact with each other at the second position can beminimized, so that the electric characteristic of the specimen can bemeasured efficiently. The base table may be movable with respect to atleast one (or each) of the first and second measuring devices.

If the first measuring device is capable of measuring the positionalrelationship between the probe and the specimen when the specimen isprevented from being irradiated with at least one of an ion beam and anelectron beam, the specimen is prevented from being damaged by the atleast one of the ion beam and the electron beam. If the second measuringdevice is capable of measuring the positional relationship between theprobe and the specimen by irradiating the specimen with at least one ofan ion beam and an electron beam, the specimen is restrained from beingdamaged by the at least one of the ion beam and the electron beam, bythe decrease of the time period for at least one of measuring thepositional relationship between the probe and the specimen at the secondposition and bringing the probe and the specimen into contact with eachother at the second position.

The first measuring device may be capable of measuring the positionalrelationship between the probe and the specimen in each of first andsecond directions perpendicular to each other, so that the distancebetween the probe and the specimen in each of first and seconddirections perpendicular to each other can be measured to increase theaccuracy for measuring the positional relationship. If the firstdirection is parallel to a thickness direction of the specimen, thefirst measuring device has a first magnification for magnifying an imagecorresponding to the positional relationship between the probe and thespecimen in the first direction and a second magnification formagnifying another image corresponding to the positional relationshipbetween the probe and the specimen in the second direction, and thefirst magnification is higher than the second magnification so that acontact or distance between the probe and specimen in the firstdirection is measurable more accurately in comparison with an overlap ordistance between the probe and specimen in the second direction, thetime period for at least one of measuring the positional relationshipbetween the probe and the specimen at the second position and bringingthe probe and the specimen into contact with each other at the secondposition can be decreased so that the electric characteristic of thespecimen can be measured efficiently.

The defective product inspection apparatus may further comprises aspecimen chamber being capable of being kept in vacuumed condition andcontaining therein the first and second positions (more preferably alsoa third position as described below) in such a manner that the probe andthe specimen are kept (continuously) in the vacuum environment of thespecimen chamber (to prevent the probe and the specimen from taken outfrom the vacuum environment, that is, the specimen chamber of vacuumedcondition containing therein the first, second and third positions),while the base table is moved between (or from) the first position and(or to) the second position, so that the specimen is preventedcompletely by the vacuumed condition of the specimen chamber from beingdamaged by an environment matter surrounding the specimen chamber.

The apparatus further may comprise a third position at which the probeis replaced by another probe, and the base table may be movable amongthe first, second and third positions in the specimen chamber, so thatthe specimen is prevented completely by the vacuumed condition of thespecimen chamber from being damaged by the replacement or exchange ofthe probe. It is preferable for increasing the efficiency for measuringthe electric characteristic of the specimen that a distance between thefirst and second positions is shorter than a distance between the secondand third positions.

The first measuring device may include at least one of an opticalmicroscope and a CCD camera.

If the probe and the specimen are capable of (manually orautomatically): being moved with respect to each other at least in afirst direction parallel to the thickness direction of the specimen,while the positional relationship between the probe and the specimen ismeasured at the first position by the first measuring device, to bepositioned to respective adjacent (relative) positions at which (adistance between the contact area of the probe and the desired area ofthe specimen is not more than a predetermined value (may be zero formaking the contact area of the probe and the desired area of thespecimen overlap at least partially each other) as seen in a firstdirection parallel to a thickness direction of the specimen and thecontact area of the probe, and/or a distance between or among the probesis as seen in the first direction is not more than a predetermined valueand being more than zero and) the desired area of the specimen areseparated from each other to form therebetween a clearance of valuebeing not more than a predetermined value (as small as possible) andbeing more than zero in the first direction, and subsequently beingmoved with respect to each other at least in the first direction tobring the contact area of the probe and the desired area of the specimeninto contact with each other while the positional relationship betweenthe probe and the specimen is measured at the second position by thesecond measuring device, the time period for at least one of measuringthe positional relationship between the probe and the specimen at thesecond position and bringing the probe and the specimen into contactwith each other at the second position can be minimized so that theelectric characteristic of the specimen can be measured efficiently, andthe specimen is restrained from being damaged at the second position (byat least one of ion beam or electron beam).

It is preferable for decreasing the time period for at least one ofmeasuring the positional relationship between the probe and the specimenat the second position and bringing the probe and the specimen intocontact with each other at the second position that the positionalrelationship between the probe and the specimen is fixed while the basetable moves from the first position to the second position.

It is preferable for correctly bringing the contact area of the probeand the desired area of the specimen into contact with each other thatthe positional relationship between the probe and the specimen is apositional relationship between the contact area of the probe and thedesired area of the specimen.

According to the invention, in a method for adjusting a positionalrelationship between a specimen and a probe to measure an electriccharacteristic of the specimen through (or with) a contact between theprobe and the specimen (so that the measured electric characteristic iscompared with a predetermined electric characteristic to judge whetherthe specimen as a product is defective or not), comprises the steps of:positioning a base table holding thereon a specimen table holding thespecimen and a probe holder holding the probe, at a first position tomeasure the positional relationship between the probe and the specimenat the first position, and subsequently positioning the base table at asecond position to measure the positional relationship between the probeand the specimen at the second position so that a contact area(preferably a front end) of the probe and a desired area of the specimenare capable of contacting each other at the second position, the basetable holds the specimen table and the probe holder at each of the firstand second positions in such a manner that the specimen table and theprobe holder are movable with respect to each other on the base table toadjust the positional relationship between the probe and the specimen,and a measuring accuracy (resolution capability, magnification or thelike) at the second position is superior to a measuring accuracy(resolution capability, magnification or the like) at the firstposition. Incidentally, the specimen table is movable with respect tothe base table, and the probe holder is movable with respect to the basetable, so that a positional relationship between the specimen table andthe base table and a positional relationship between the probe holderand the base table are adjustable independent of each other, and one ofthe positional relationship between the specimen table and the basetable and the positional relationship between the probe holder and thebase table is adjustable when the other one the positional relationshipbetween the specimen table and the base table and the positionalrelationship between the probe holder and the base table is stationary.

Since the base table holds the specimen table and the probe holder ateach of the first and second positions in such a manner that thespecimen table and the probe holder are movable with respect to eachother on the base table to adjust the positional relationship betweenthe probe and the specimen, and the measuring accuracy (resolutioncapability) at the second position is superior to a measuring accuracy(resolution capability) at the first position, a time period which isneeded for measuring the positional relationship between the probe andthe specimen at the second position with the measuring accuracy(resolution capability) superior to the measuring accuracy (resolutioncapability) at the first position can be decreased by the measurement atthe first position, so that the electric characteristic of the specimencan be measured efficiently.

It is preferable for minimizing the time period for at least one ofmeasuring the positional relationship between the probe and the specimenat the second position and bringing the probe and the specimen intocontact with each other at the second position, that the probe and thespecimen are capable of being moved with respect to each other at leastin a first direction parallel to the thickness direction of the specimenat the first position, while the positional relationship between theprobe and the specimen is measured, to be positioned to respectiveadjacent (relative) positions at which (a distance between the contactarea of the probe and the desired area of the specimen is not more thana predetermined value (may be zero for making the contact area of theprobe and the desired area of the specimen overlap at least partiallyeach other) as seen in a first direction parallel to a thicknessdirection of the specimen and/or a distance between or among the probesas seen in the first direction is not more than a predetermined valueand being more than zero, and) the contact area of the probe and thedesired area of the specimen are separated from each other to formtherebetween a clearance of value being not more than a predeterminedvalue (as small as possible) and being more than zero in the firstdirection, and subsequently the probe and the specimen are moved withrespect to each other at least in the first direction at the secondposition to bring the contact area of the probe and the desired area ofthe specimen into contact with each other while the positionalrelationship between the probe and the specimen is measured.

If at the first position, the positional relationship between the probeand the specimen is measured when the specimen is prevented from beingirradiated with at least one of an ion beam and an electron beam, thespecimen is prevented from being damaged by the at least one of the ionbeam and the electron beam. If at the second position, the positionalrelationship between the probe and the specimen is measured whileirradiating the specimen with at least one of an ion beam and anelectron beam, the specimen is restrained from being damaged by the atleast one of the ion beam and the electron beam, by the decrease of thetime period for at least one of measuring the positional relationshipbetween the probe and the specimen at the second position and bringingthe probe and the specimen into contact with each other at the secondposition.

If at the first position, the positional relationship between the probeand the specimen in each of first and second directions perpendicular toeach other is measured, the first direction is parallel to a thicknessdirection of the specimen, and a first magnification for magnifying animage corresponding to the positional relationship between the probe andthe specimen in the first direction is higher than a secondmagnification for magnifying another image corresponding to thepositional relationship between the probe and the specimen in the seconddirection (so that a contact or distance between the probe and specimenin the first direction is measurable more accurately in comparison withan overlap or distance between the probe and specimen in the seconddirection), a contact or distance between the probe and specimen in thefirst direction is measurable more accurately in comparison with anoverlap or distance between the probe and specimen in the seconddirection, and the time period for at least one of measuring thepositional relationship between the probe and the specimen at the secondposition and bringing the probe and the specimen into contact with eachother at the second position can be decreased so that the electriccharacteristic of the specimen can be measured efficiently.

If a vacuum environment is kept around the base table so that the probeand the specimen are kept (continuously) in the vacuum environment (toprevent the probe and the specimen from taken out from the vacuumenvironment, that is, the specimen chamber of vacuumed conditioncontaining therein the first, second and third positions) while the basetable is moved between (or from) the first position and (or to) thesecond position, the specimen is prevented completely by the vacuumedcondition of the specimen chamber from being damaged by an environmentmatter surrounding the specimen chamber.

If the base table is moved among the first position, the second positionand a third position at which the probe is replaced by another probe inthe specimen chamber, the specimen is prevented completely by thevacuumed condition of the specimen chamber from being damaged by thereplacement or exchange of the probe.

If the positional relationship between the probe and the specimen isfixed while the base table moves from the first position to the secondposition, the time period for at least one of measuring the positionalrelationship between the probe and the specimen at the second positionand bringing the probe and the specimen into contact with each other atthe second position can be decreased.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a defective product inspectionapparatus.

FIG. 2A is a horizontal projection view of the defective productinspection apparatus and FIG. 2B is a side view thereof.

FIG. 3 is a side view of the defective product inspection apparatus inwhich a slide base is drawn out from a specimen chamber.

FIG. 4 is a horizontal projection view showing an arrangement of probes.

FIG. 5A is a schematic oblique projection view showing a probe holderand a probe unit, and FIG. 5B is a side view of an assembly of the probeholder and the probe unit.

FIG. 6 is a schematic oblique projection view showing a movable stage.

FIG. 7 is a schematic cross sectional view showing a vertically part ofthe movable stage.

FIG. 8A is a schematic side view of the movable stage, and FIG. 8B is across sectional view taken along a line A-A′ in FIG. 8A.

FIG. 9 is a partially cross sectional side view showing the movablestage and a grounded line.

FIG. 10A is a schematic partially cross sectional view showing themovable stage under an electron microscope for finish or finepositioning between the specimen and the probe with projecting theelectron beam to the specimen, FIG. 10B is a schematic partially crosssectional view showing the movable stage under an optical microscopeenabling a rough approach or positioning between the specimen and theprobe without projecting the electron beam to the specimen, and FIG. 10Cis a schematic partially cross sectional view showing the movable stageunder a probe exchange mechanism.

FIG. 11A is an oblique projection view showing a probe exchange rod anda probe holder, and FIG. 11B is an enlarged view of A region of FIG.11A.

FIG. 12A is a schematic view showing a positional relationship as seenin a vertical direction between the probe and the specimen positionedroughly with respect to each other under the optical microscope, FIG.12B is a schematic view showing the positional relationship as seen in ahorizontal direction between the probe and the specimen positionedroughly with respect to each other under the optical microscope, andFIG. 12C is an extremely enlarged schematic view showing the positionalrelationship as seen in the vertical direction between the probe and thespecimen positioned finely with respect to each other under the electronmicroscope.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, a defective product inspection device 1 has aspecimen chamber 7 containing a specimen stage including a specimenholder 2 on which a specimen is to be held, and a specimen holderreceiver 17 holding the specimen holder 2, and a probe stage 6 includinga probe unit 33. An electronic optical device 4 (a charged particleapparatus) such as an SEM (scanning electron microscope), a focused ionbeam (FIB) device or the like including an ion pump 44 is arranged on aframe of the specimen chamber 7 to opposite to the specimen holder 2.Further, a probe rough-approaching image forming device 10 is arrangedin the vicinity of the electronic optical device 4. A charged particlebeam (electron beam or ion beam) is projected from the electronicoptical device 4 toward the specimen holder to monitor movements of thespecimen and a probe 3.

The probe rough-approaching image forming device 10 arranged in thevicinity of the electronic optical device 4 on an upper surface of theframe of the specimen chamber 7 has a probe rough-approaching opticalmicroscope and a CCD camera for obtaining an image so that a conditionin rough approach of the probe 3 with respect to the specimen ismonitored by obtaining its image. Further, the probe rough-approachingimage forming device 10 has a probe rough-approaching image formingdevice 10 a for monitoring in a vertical direction and a proberough-approaching image forming device 10 b for monitoring in ahorizontal direction, so that the condition in rough approaching betweenthe prove and the specimen can be monitored securely in two directionsperpendicular to each other. In this case, a magnification of the proberough-approaching image forming device 10 b for magnifying the imagecorresponding to the condition in rough approaching as seen in thehorizontal direction is made higher than a magnification of the proberough-approaching image forming device 10 a for magnifying the imagecorresponding to the condition in rough approaching as seen in thevertical direction, because the image corresponding to the condition inrough approaching obtained by the probe rough-approaching image formingdevice 10 a needs to include a plurality of the probes 3 which need tobe approached each other and horizontally positioned over respectiveareas of the specimen so that at least one electric characteristic ofthe specimen is detected from the areas of the specimen after the probes3 are brought into contact with the areas of the specimen respectively.Each of the probes is moved downwardly to a position adjacent to thespecimen while monitoring the image corresponding to the condition inrough approaching as seen in the horizontal direction, and the probesare moved to be adjacent to each other and be separated from each otherwith a slight distance therebetween or thereamong as seen in thevertical direction. Subsequently, each of the probes is brought intocontact with the respective one of the areas of the specimen by movingdownwardly each of the probes while monitoring a difference between afocusing condition of each of the probes and a focusing condition of thecorresponding one of the areas of the specimen to be decreased in animage as seen in the vertical direction formed by the electronic opticaldevice 4, that is, while monitoring a focusing position of theelectronic optical device 4 at which each of the probes is focused and afocusing position of the electronic optical device 4 at which thecorresponding one of the areas of the specimen or an area closelyadjacent to the corresponding one of the areas of the specimen isfocused. If a distance between each of the probes and the correspondingone of the areas of the specimen is made as small as possible before thedownward movement of each of the probes on the basis of the image formedby the electronic optical device 4, a time period for the downwardmovement of each of the probes for the contact between each of the probeand the corresponding one of the areas of the specimen on the basis ofthe image formed by the electronic optical device 4 can be small todecrease an amount of the charged particle beam with which the specimenis irradiated by the electronic optical device 4. Therefore, themagnification of the probe rough-approaching image forming device 10 bis made higher than the magnification of the probe rough-approachingimage forming device 10 a to improve an accuracy for measuring apositional relationship between each of the probes and the correspondingone of the areas of the specimen.

A stage includes a base table 49 on which a specimen stage 50 on whichthe specimen holder 2 for holding the specimen is mounted and the probeunit 33 are mounted, and a base plate 48 on which the base table 49 isguided linearly and moved horizontally to position a combination of aset of the probes and the specimen at desired one of a fine or finishpositioning position just under the electronic optical device 4 formeasuring extremely accurately the positional relationship between eachof the probes (preferably the front end contacting areas of the probes)and the corresponding one of the areas of the specimen and bringing eachof the probes into contact with corresponding desired electrode of thespecimen by moving each of the probes (preferably with an extremelyslight adjustment of the positional relationship between each of theprobes and the corresponding desired electrode of the specimen as seenin the thickness direction of the specimen), a rough-approachingpositioning position just under the probe rough-approaching imageforming device 10 for measuring the positional relationship between oramong the probes and the positional relationship between each of theprobes and the specimen and positioning each of the probes or the set ofthe probes with respect to the specimen to make a distance between oramong the probes to be included by an area as seen in the directionparallel to the thickness direction not more than a visible ormeasurable scope of the electronic optical device 4 and to make adistance between each of the probes and the specimen or a distancebetween the set of the probes and the specimen as seen in anotherdirection perpendicular to the thickness direction not more than apredetermined value and more than zero so that each of the proves andthe set of the probes are separated slightly (as shortly as possiblewhile keeping a minimum distance or clearance therebetween) from thespecimen as seen in another direction perpendicular to the thicknessdirection of the specimen, and a probe exchange position just under aprobe exchange chamber 9 for removing desired one of the prove holders31 including the respective probes 3 from corresponding one of the probeunits 33 to be withdrawn into the probe exchange chamber 9 andsubsequently bringing a substitute one of the probe holders 31 from theprobe exchange chamber 9 to be set onto the corresponding one of theprobe units 33. The stage is attached to a side surface of the specimenchamber 7 through a plate 71. As shown in FIG. 2, the plate 71 ismovably supported on the specimen chamber 7 by a guide connecting plate71 a and a roller guide 71 b. As shown in FIG. 3, the stage is drawn outof the specimen chamber 7 along the roller guide 71 b when a maintenanceof the stage is done or the probe unit is exchanged. Guide blocks 48 aattached to a lower surface of the specimen chamber 7 support verticallythe stage through sliding members 48 b of low-friction high polymermaterial between upper surfaces of the guide blocks 48 a and a lowersurface of the base plate 48.

The probe stage 6 has the probe units 33 including the probe holders 31for holding the probes 3 respectively, a probe unit base 34 on which theprobe units 33 are mounted and a probe unit bracket 35 connecting theprobe unit base 34 to the base table 49. Each of the probe units 33 cangenerates a movement of respective one of the probes 3 in threedirections perpendicular to each other with respect to the probe unitbase 34 fixed to the base table 49. The base plate 48 can be fixed tothe side wall of the specimen chamber 7 by a fixing member 47. Thespecimen chamber 7 includes a specimen exchange chamber 8 and the probeexchange chamber 9.

The plate 71 includes a feed-through to supply a signal for controllingthe probe driving motion of each of the probe units 33, and a signal forcontrolling a motion of each of x, y, z tables 61, 62, 63 of thespecimen stage 50 into the specimen chamber 7.

Although the specimen exchange chamber 8 is arranged on a right sidesurface in FIG. 1, the specimen exchange chamber 8 may be arranged at afront side surface in the vicinity of the electronic optical device 4 sothat the specimen can be exchanged easily when the specimen table isunder the electronic optical device 4. An inside of the specimenexchange chamber 8 and an inside of the specimen chamber 7 are connectedto each other by a gate valve 21. The inside of the specimen exchangechamber 8 is connected by a dry pump 52 to be vacuumed. Therefore, theexchange of the specimen holder with the specimen thereon can beperformed by a transfer member 29 while a vacuum condition is kept inthe specimen chamber 7.

The probe exchange chamber 9 is arranged adjacently to the electronicoptical device 4 and the probe rough-approaching image forming device 10a while its distance from the probe rough-approaching image formingdevice 10 a is smaller than its distance from the electronic opticaldevice 4. An inner side of the probe exchange chamber 9 is connected tothe inside of the specimen chamber 7 through a gate valve 23. The probeexchange chamber 9 is fluidly connected to a turbo molecular pump (TMP)51 and the dry pump (DP) 52 connected to the turbo molecular pump toperform a vacuuming operation. While maintaining a high vacuum in thespecimen chamber 7, the probe holder 31 is exchanged by an exchangemechanism 55. The specimen chamber 7 is fluidly connected to the TMP 11through a gate valve 53 and the TMP 11 is connected to DP 12. A frame ofthe specimen chamber 7 is supported by a bracket 25 shown by analternate long and short dash line. A control device 13 including aprobe unit control part and a stage control part and another controldevice 13A for controlling a high vacuuming operation of the TMP 11 andDP 12 are arranged. The control device 13A controls also TMP 51 and DP52.

Further, the defective product inspection apparatus 1 includes a displaydevice 14 including an image display part 15 and an image displaycontrol part 16, and a probe operation signal and a stage operationsignal from the image display control part 16 are transmitted to theprobe unit control part and the stage control part to control the probeunits 33 and the stage.

The probe is exchanged, after the x and Y tables of the probe unit to beexchanged are positioned at respective predetermined positions (forexample, back end positions), and the z table thereof is positioned at apredetermined position (for example, upper most end position).

The specimen stage 50 is driven to position an area of the specimenwhich should be made visible on the image display part 15 for displayingthe image generated by the electronic optical device 4, that is, needsto be contacted by the probes, into the visible or measurable scope ofthe electronic optical device 4 for monitoring both the set of theprobes and the area of the specimen after the base table 49 is moved onthe base plate 48 and the X-Y tables 64 and 65 are driven so that theset of the proves is positioned in the visible or measurable scope ofthe electronic optical device 4, and subsequently each of the probes 3is brought into contact with the corresponding one of the electrodes onthe area of the specimen by driving the x, y and z tables of thecorresponding one of the probe units 33 while monitoring each of theprobes and the specimen on the image display part 15. The condition incontact and distance between the probe and the electrode of the specimenin the direction parallel to the thickness direction of the specimen ismeasurable from the focusing conditions of the electronic optical device4 on the front end (contact area) of the probe and the electrode surfaceor a surface area of the specimen closely adjacent to the electrodesurface, that is, a focusing position of the electronic optical device 4at which the front end (contact area) of the probe is focused and afocusing position of the electronic optical device 4 at which theelectrode surface or the surface area of the specimen closely adjacentto the electrode surface is focused.

A drive mechanism for the probes and the stages are not necessarilylimited, but the drive mechanism for the probes may have apiezo-electric element, DC motor or ultrasonic motor, and the drivemechanism for the stages may have a pulse motor, DC motor or ultrasonicmotor.

1. Structure and Operation of Each Element

(1) Probe 3 and Probe Unit 33

As shown in FIG. 4, the probes 3 (six in FIG. 4) are held by the probeholders 31 respectively to form six of the probe units 31 respectivelyto be supported on the probe unit base 34.

FIG. 5 shows in detail the probe holder and the probe unit. As shown in(a) part of FIG. 5, the probe holder 31 is inserted into the z table 83of the probe unit 33 and held stationarily thereto by a plate spring 84.An assembled condition of the probe unit 33 is shown in (b) part of FIG.5. The probe holder 31 includes the probe 3 to be contacted with thespecimen, a probe support bar 85 for fixing the probe 3 and a probe arm86 for fixing the probe support bar 85. The probe support bar 85 has atubular shape. The probe arm 86 includes a support bar fixing member 87,an insulating ring 88, a connection pipe 89 and an insulating ring 90,and the insulating ring 90 is connected to a probe holder base 91. Thesupport bar fixing member 87 is isolated from the connection pipe 89 bythe insulating ring 88, and the connection pipe 89 is isolated from theprobe holder base 91 by the insulating ring 90. The support bar fixingmember 87 extends in the connection pipe 89 to a back surface of theprobe holder base 91 to contact a probe signal outlet electrode 101 whenthe probe holder 31 is inserted in the z table 83. The probe signaloutlet electrode 101 is isolated from the z table 83. The connectionpipe 89 contacts a guard signal outlet electrode 102 when the probeholder 31 is inserted in the z table 83. A grounded signal is obtainedfrom the z table 83. The probe signal from the probe signal outletelectrode 101, the guard signal from the guard signal outlet electrode102 and the grounded signal from the z table 83 are connected to athree-phase coaxial cable, taken out from the specimen chamber 7 througha three-phase coaxial hermetic connector mounted on the specimen chamber7, and connected through the three phase coaxial cable to an electriccharacteristic measuring apparatus such as a semiconductor parameteranalyzer or the like to measure the electric characteristic.

(2) Stage

The structure of the stage is shown in FIGS. 6-9. The stage includes thebase table 49 (as the claimed base table) and the specimen stage 50.

(a) Specimen Stage 50

The specimen stage 50 includes the y table 62, x table 61 and z table63, 63 a to be driven respective driving mechanisms to be moved inrespective y, x and z directions to align the area of the specimenwithin the visible or measurable scope of the electronic optical device4. Incidentally, the positional relationship among the probes isadjusted by the x and y tables of the prove units 33 in accordance withthe positional relationship among the electrodes on the area of thespecimen to align the probes respectively with the electrodes on thearea of the specimen in the thickness direction of the specimen underthe electronic optical device 4 after the positional relationshipbetween or among the probes is adjusted under the proberough-approaching image forming device 10 so that the probes areincluded by an area as seen in the thickness direction of the specimennot more than the visible or measurable scope of the electronic opticaldevice 4, and each of the probes is driven in the thickness direction ofthe specimen by corresponding one of the z tables of the prove units 33to be brought into contact with the corresponding one of the electrodesunder the electronic optical device 4. Under the electrodes under theelectronic optical device 4, each of the probes is moved by the y and xtables of the corresponding one of the prove units 33 to make each ofthe probes and the corresponding one of the electrodes overlap eachother as seen in the thickness direction. The x and y tables of theprove units 33 are used to adjust the positional relationship among theprobes in accordance with the positional relationship among the desiredelectrodes of the specimen as seen in the thickness direction of thespecimen, and the z tables of the prove units 33 are used to bring eachof the probes into contact with the corresponding one of the desiredelectrodes of the specimen. The x and y tables of the specimen stage 50are used to align the area including the desired electrodes of thespecimen with the visible or measurable scope of the electronic opticaldevice 4, and the z table of the specimen stage 50 may be used to make adistance between the area including the desired electrodes of thespecimen and the set of probes (the set of the contact areas of theprobes to be positioned in accordance with the positional relationshipamong the desired electrodes of the specimen) as small as possible underthe probe rough-approaching image forming device before bringing each ofthe probes into contact with the corresponding one of the desiredelectrodes of the specimen by the z tables of the prove units 33 underthe electronic optical device 4.

The y and x tables 62 and 61 are driven by the respective DC motorsthrough respective ball-screws in the specimen chamber and guided bycross-roller guides. As shown in FIG. 7, the z table 63 is moved bydriving a ball screw 63 e by the DC motor 63 b mounted on the z tablebody 63 a through bevel gears 63 g, 63 h and shafts 63 c, 63 d. The ztable is guided linearly by a cross-roller guide. The specimen holder 2for holding a specimen 2 a is fixed to the specimen holder receiver 17mounted on the z table 63. Therefore, the specimen 2 a is movable withrespect to an electron beam 69 in x, y and z directions. The specimenholder 2 on the z table 63 is movable among a measuring position, aspecimen exchange position and a probe exchange position. The measuringposition is a position at which a distance between the probe and thespecimen 2 a is decreased to be made as small as possible under theprobe rough-approaching image forming device 10 and the probe is broughtinto contact with the specimen 2 a under the electronic optical device4, the specimen exchange position is a position lower than the measuringposition, and the probe exchange position is a position lower than thespecimen exchange position, so that an undesirable contact between theprobe 3 and the specimen 2 a is prevented during each of the probeexchange operation and the specimen exchange operation. The stage 50 mayincludes a positional sensor such as a linear scale, an encoder or thelike to measure quantitatively the position of each of the tables of thestage 50 during the operations, so that an accuracy and repeatability ofthe movement is obtainable. Examples of arrangement of the positionalsensors are shown in FIGS. 7 and 8. The positional condition of the ztable is measurable by the encoder 63 f connected to the shaft 63 c asshown in FIG. 7. The positional conditions of the e table 61 and y table62 are measurable by the linear scales mounted as shown in FIG. 8. Thelinear scale has mirrors 61 a, 62 a mounted on the x table 61 and ytable 62 and sensor elements 61 b, 62 b. In this case, the encoder formeasuring the rotary angle of the DC motor is used for the z table, andthe linear scales are used for the x table 61 and y table 62, but theencoders, linear scales or combinations thereof may be used for all ofthe tables.

During the monitoring by the SEM, the specimen 2 a mounted on thespecimen stage 50 is electrically grounded through the specimen stage 50and the specimen chamber 7 to prevent an effect by a charging up. Whenan electric characteristic of the specimen 2 a is measured, the specimen2 a is preferably isolated electrically from the specimen stage 50 andthe specimen chamber 7. Further, for preventing the effect of thecharging up, a beam blanking is effective. For the electricalinsulation, as shown in FIG. 9, an insulating member 18 is arrangedbetween the specimen holder receiver 17 and the z table 63, the specimenholder receiver 17 with the specimen 2 a thereon is connected to a cable20, and the cable 20 extends from the fixing member 47 through the plate71 to an outside of the vacuumed environment so that the cable 20 isconnected to a grounded terminal through a switch 19. By this structure,during the SEM monitoring, the specimen 2 a is grounded by operating theswitch 19 to prevent the effect caused by the noise. Further, byconnecting the cable 20 through the switch 19 not to the ground but toan electric characteristic measuring device, the electric characteristicof the specimen 2 a such as absorption current or the like is measurablewithout the effect of the noise from the specimen stage 50 and thespecimen chamber 7. Further, the specimen holder receiver 17 mayincludes a guard electrode and a grounded electrode similarly to theprobe units 33 and the probe holders 31 as shown in FIG. 5, so that thecable is connected through the three phase coaxial cable to the outsideof the vacuumed environment. Therefore, the electric isolation for thespecimen 2 a is improved.

(b) Base Table 49

With making reference to FIG. 10, a process for positioning the specimen2 a and the probes 3 in the specimen chamber is explained.

As shown in FIG. 6, the base table 49 includes the Y table 64 and Xtable 65 to be positioned in y and x directions respectively. The stage50 and each of the prove holders 31 are mounted on the base table 49 toadjust and fix the positional relationship between the specimen 2 a andeach of the probes on the base table 49.

On the base table 49, the probe units 33 forming the probe stage 6, theprobe unit base 34 for supporting the probe units 33 and the probe unitbracket 35 are mounted. Each of the prove units 33 can position theprobe in y, x and z directions through the prove holder 31 supported byeach of the prove units 33.

As shown in FIG. 10, the base table 49 is moved on the base plate 48along a linear guide by a ball-screw and a servo motor to positionbriefly a combination of the specimen and the set of the probes withrespect to each of the probe rough-approaching image forming device 10,the electronic optical device 4 and the probe exchange chamber 9. The Ytable 64 and X table 65 of the base table 49 position accurately thecombination of the specimen and the set of the probes with respect toeach of the probe rough-approaching image forming device 10, theelectronic optical device 4 and the probe exchange chamber 9.

Therefore, the combination of the specimen and the set of the probes arepositioned to each of A position under the electronic optical device 4,B position under the probe rough-approaching image forming device 10 andC position under the probe exchange chamber 9 while the vacuumedenvironment surrounding the combination of the specimen and the set ofthe probes is being kept during the movement of the combination of thespecimen and the set of the probes among the A, B and C positions withinthe specimen chamber.

(3) SEM

The SEM arranged on the upper portion of the specimen chamber is anexample of the electronic optical device 4 for monitoring the positionalrelationship between each of the probes (each of the contact areas ofthe proves) and the corresponding one of the electrodes of the specimento bring each of the probes in contact with the corresponding one of theelectrodes of the specimen. The vacuuming operation for the SEM isperformed by the ion pump 44. On the other hand, the proberough-approaching image forming device 10 including the opticalmicroscope monitors the positional relationship between each of theprobes and the corresponding one of the electrodes of the specimenwithout irradiating the specimen to bring each of the probes to aposition close to the corresponding one of the electrodes of thespecimen with making a distance (more than zero) between each of theprobes and the corresponding one of the electrodes of the specimen assmall as possible.

(4) Specimen Chamber 7

The specimen chamber 4 includes an upper cover and a specimen chambercase as the frame, the base 48 is attached to the plate 71 through thefixing member 47 at the side surface of the specimen chamber case, theprobe units 33 are mounted on the base table 49 in the specimen chamber,and the specimen exchange chamber 8 is attached to another side surfaceof the specimen chamber case. The probe rough-approaching image formingdevice 10, the electronic optical device 4 and the probe exchangechamber 9 are mounted on the upper cover. The specimen chamber 7 isfixed to a bearing plate mounted on a vibration absorbing mount on thebracket 25. The specimen chamber 7 is vacuumed by the turbo molecularpump (TMP) 11 and the dry pump (DP) 12.

(5) Optical Microscope for Rough-Approaching, CCD Camera andRough-Approaching Image Forming Device

The specimen 2 a whose electrical characteristic needs to be measured isa semiconductor including plugs generally connected a gate, a source, adrain and a well respectively to be connected by the probesrespectively. The plug may have a minimum diameter of tens ofnanometers, so that a SEM with high resolution is necessary for bringingthe probe into contact with the plug. However, by irradiating thesemiconductor specimen with the electron and/or ion beam, there is aprobability of that the semiconductor specimen is damaged, so that it ispreferable for a time period of irradiating the semiconductor specimenwith the electron and/or ion beam to be made as short as possible.Therefore, on the basis of the image of the probe rough-approachingimage forming device 10 displayed on the image display part 15, adistance between each of the probes and corresponding one of the plugs(electrodes) of the specimen as seen in the thickness direction of thesemiconductor specimen is made as small as possible or preferably zero,and a gap or clearance therebetween as seen in a direction perpendicularto the thickness direction is made as small as possible but is preventedfrom being zero. This operation is performed while an image showing thepositional relationship between the probes and the specimen surface asobtained by the probe rough-approaching optical microscope and the CCDcamera attached thereto and displayed on the image display portion 15 ismonitored.

The magnification on the image display portion 15 is tens to form animage including the specimen 2 a and the probes 3 adjacent to each otheras close as possible.

A light source is arranged in the vicinity of the proberough-approaching optical microscope. The monitoring by the proberough-approaching optical microscope and CCD camera and the light supplyfrom the light source into the specimen chamber is performed through awindow aperture 39 as shown in FIG. 1.

(6) Specimen Exchange Chamber 8

The specimen exchange chamber 8 is arranged to exchange the specimen 2 awhile keeping the environment vacuum condition surrounding the specimen2 a in the specimen chamber 7 and vacuumed by the dry pump 52. Thespecimen exchange chamber 8 can be isolated fluidly from the specimenchamber 7 by the gate valve 21. When the specimen 2 a is introduced intothe specimen chamber 7, a male screw of a front end of an exchange bar29 as a transfer member for the specimen 2 a and the specimen holder 2is screwed into a female screw of the specimen holder 2 with thespecimen 2 a thereon, the gate valve 21 is opened, and the specimenholder 2 is inserted onto the specimen holder receiver 17 attached to anupper end of the z table 63 of the specimen stage 50. When the specimen2 a is taken out of the specimen chamber, a reverse operation isperformed. Therefore, a time period for the specimen exchange can bedecreased.

(7) Probe Exchange Chamber 9

The probe exchange chamber 9 is arranged to exchange the probe 3 whilekeeping the environment vacuum condition surrounding the probe 3 in thespecimen chamber 7 so that a time period for the probe exchange isdecreased. The probe exchange chamber 9 can be isolated fluidly from thespecimen chamber 7 by the gate valve 23. The probe exchange chamber 9 isvacuumed by the turbo molecular pump 51 and the dry pump 52. The turbomolecular pump 51 is used to accelerate a vacuuming operation for theprobe exchange chamber 9, because if the vacuuming operation for theprobe exchange chamber 9 is brought about by the dry pump 52 without theturbo molecular pump 51, a great volume of the probe exchange chamber 9in which a pressure cannot be decreased sufficiently within a short timeperiod by the dry pump 52 without the turbo molecular pump 51 causes agreat increase of the inner pressure of the specimen chamber 7 when thegate valve 23 is opened to exchange the probe 3 so that a time periodfor making the pressure in the specimen chamber 7 at the same value asthe previous pressure before opening the gate valve 23 becomes long.

In the probe exchange chamber 9, a stocker (not shown) for holding theprobe holders 31 is arranged and moved by a ball-screw with respect to aprobe exchange bar 92. The probe holder 31 is moved below the probeexchange bar 92 to be withdrawn from the stocker or contained in thestocker. A latch key 96 at a lower end of an exchange rod 94 arranged ina probe exchange bar outer tube 93 coaxial with the probe exchange bar92 is rotated by 90 degrees to engage with a latch receiver 95 on theprobe holder 31 to be connected to the probe exchange bar 92. Theexchange rod 94 is rotated by 90 degrees in a reverse direction todisengage the latch key 96 from the latch receiver 95. The stockerincluding the used probe holders 31 is taken out of the probe exchangechamber 9, and unused ones of the probe holders 31 are inserted onto thestocker to be introduced into the probe exchange chamber 9.

When the probe holder 31 is transferred from the stocker to the probeunit 33, the latch key 96 of the probe exchange rod 94 is engaged withthe latch receiver 95 on the probe holder 31, and the probe exchange bar92 is moved upward by a rack-and-pinion mechanism to withdraw the probeholder 31 from the stocker. The gate valve 23 is opened and the probeexchange bar 92 is moved downward to introduce the probe holder 31 intothe specimen chamber. As shown in FIG. 5, the holder receiver isarranged on the z table 83 of the probe unit 33. The base table 49 isdriven to move the holder receiver below the transferred probe holder31, the probe exchange bar 92 is rotated to make orientations of theholder receiver and the probe holder 31 consistent with each other, andthe exchange bar 92 is moved downward to insert the probe holder 31 intothe holder receiver. The latch key 96 is disengaged from the latchreceiver 95, the probe exchange bar 92 is moved upward to be withdrawninto the probe exchange chamber 9, and the gate valve 23 is closed.

2. Control System

The SEM, the probe units 33 and the tables of the stages are controlledby respective control circuits and computers contained by the controldevice 13. The SEM, the probe units 33 and the tables of the stages arecontrollable from a operating panel or GUI on the monitor.

The control device 13 includes a stage controller for controlling thetables of the stages, and a probe controller for controlling the probeunits 33 independent of the stages. The image control part 16 includes asecondary electron detector control part, a control part for theelectron beam emitting optical system and so forth. In addition, acalculation treatment part has a function of displaying an image showingthe specimen holder, the specimen 2 a and the positional relationshipbetween the proves and the specimen 2 a.

The probe units 33 and the tables of the stages are driven by operatingan operating display of the image display part to supply an operatingsignal through the image display control part to the probe unit controlpart and the stage control part. Alternatively, an operating panelincluding a joy-stick may be used to drive the units 33 and the tablesof the stages.

(1) SEM

The electron beam generated by an electron gun is emitted through acondensing lens and an objective lens to the specimen 2 a to beirradiated, and the secondary electron generated from the specimen 2 ais detected by the secondary electron detector to generate a signal sothat the signal is electrically treated variously in the display to forman image of the specimen surface on the monitor on the image displaypart 15 of the display device 14.

(2) Probe Unit 33

A signal for controlling each of the operations of the x, y and z tablesof each of the probe units 33 from the control circuit 13 in the bracket25 as shown in FIG. 1 is supplied to each of the probe units 33 in thespecimen chamber 7 through a feed-through attached the plate 71 of thestages. Input signals supplied to the specimen 2 a through the probes 3attached to the probe holders 31 and output signals generated from thespecimen 2 a are transmitted with respect to a semiconductor parameteranalyzer through a three phase coaxial hermetic connector attached tothe specimen chamber 7.

(3) Stages

Signals generated by the control circuit in the bracket 25 to controlthe operations of the x, y and z tables 61, 62 and 63 of the specimenstage 50 on the base plate 49 are supplied to the specimen stage 50 inthe specimen chamber through the feed-through attached to the plate 71.Signals for controlling the operations of the x and y tables 64 and 65are also supplied to the base plate 49 through the feed-through attachedto the plate 71.

3. Display Device 14

The display device 14 displays a rough-approaching image taken by theprobe rough-approaching image forming device 10, a contacting imagetaken by the electron optical device 4 to show a positional relationshipbetween each of the probes and the specimen brought into contact witheach other, the probe operating image and an image showing a sequence ofthe operating.

The user operates the probes 3 and the specimen 2 a to be positionedaccurately with respect to each other along the sequence of theoperating displayed on the display device 14, while monitoring therough-approaching image and the contacting image.

As shown in FIG. 12A, the rough-approaching image taken by the proberough-approaching image forming device 10A shows the positionalrelationship between each the probes and the specimen as seen in thethickness direction of the specimen with the magnification of, forexample, 10. As shown in FIG. 12B, the rough-approaching image taken bythe probe rough-approaching image forming device 10B shows thepositional relationship between each the probes and the specimen as seenin the direction perpendicular to the thickness direction of thespecimen with the magnification of, for example, 25 increased by 2.5times in comparison with the magnification of the rough-approachingimage taken by the probe rough-approaching image forming device 10A toenable a distance between each of the probes 3 and the specimen 2 a asseen in the direction perpendicular to the thickness direction of thespecimen to be made as small as possible but to be prevented fromdecreasing to zero. As shown in FIG. 12C, the contacting image taken bythe electron optical device 4 shows the positional relation ship betweeneach of the probes 3 (each of the contact areas of the probes) and thecorresponding one of the electrodes or plugs 100 of the specimen 2 a tobe brought into contact with each other, with the magnification ofthousands to ten-thousands. The electrodes or plugs 100 are connectedrespectively to the gate, source, drain and so forth in the specimen 2a.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A method for exchanging a probe, comprising the steps of: opening a gate valve for seperating a probe exchange chamber and a specimen chamber from each other, transferring a probe holder from the probe exchange chamber by an exchange member arranged in the probe exchange chamber to the specimen chamber connected to the probe exchange chamber when the gate valve is opened; and mounting the probe holder onto a specimen stage in a specimen chamber.
 2. The method according to claim 1, wherein the specimen stage is moved in the specimen chamber from a position for inspecting the specimen to another position for mounting the probe holder onto the specimen stage.
 3. The method according to claim 1, wherein the exchange member is rotated to make a latch part of the exchange member engage with a latch catcher of the probe holder, and is moved vertically downward to mount the probe holder to the specimen stage.
 4. The method according to claim 1, wherein the probe exchange chamber and the specimen chamber are fluidly isolatable from each other by the gate valve.
 5. A defective product inspection apparatus for inspecting a product as a specimen, comprising: a specimen stage for holding the specimen theron, a specimen chamber for containing the specimen stage therein, a probe contactable with the specimen in the specimen chamber, a probe exchange chamber for containing the probe holder therein, a gate valve capable of opening to connect the specimen chamber and the probe exchange chamber to each other, and a transferring mechanism for transferring the probe holder from the probe exchange chamber into the specimen chamber when the gate valve is opened.
 6. The defective product inspection apparatus according to claim 5, wherein the specimen stage is movable in the specimen chamber from a position for inspecting the specimen to another position for mounting the probe holder onto the specimen stage.
 7. The defective product inspection apparatus according to claim 5, wherein the exchange member is rotatable to make a latch part of the exchange member engage with a latch catcher of the probe holder, and is movable vertically downward to mount the probe holder onto the specimen stage.
 8. The defective product inspection apparatus according to claim 5, wherein the probe exchange chamber and the specimen chamber are capable of being isolated fluidly from each other by the gate valve. 